Refrigeration is a necessary expense for most perishable food and beverage products. Given foods’ margin pressures, controlling and possibly reducing refrigeration costs can mean the difference between profit and loss. Fortunately, technology is providing remedies to the cost squeeze.
In industrial freezing, mechanical refrigeration using ammonia is the go-to option, although the risk of ammonia leaks that can harm workers and destroy products is a constant concern. The danger can be minimized with a cascade system that draws much less energy and can attain much lower temperatures, giving companies the option to increase throughput in the same footprint.
With cascade refrigeration, an ammonia loop in a contained area is the high-temperature side, helping the carbon dioxide refrigerant that chills processing and storage areas descend to temperatures below -50°F. “It’s not cookie-cutter technology,” says one proponent, “but it’s proven.”
High electricity costs in Europe have helped make cascade systems mainstream. Relatively low energy prices in North America have slowed deployment. The technology got a boost in 2003 when Nestle commissioned a Stouffer’s frozen foods facility in Jonesboro, Ark. Cascade added cost to the 525,000-sq.-ft. project, but the company wanted to demonstrate its commitment to sustainable production and give itself a hedge against electricity price increases.
Federalsburg, Md.-based M&M Refrigeration jumped into the CO2 space in 2004, just in time to feel the impact of some suboptimal installations that followed. According to CEO Duane Marshall (www.mmrefrigeration.com), M&M’s first cascade client demanded a performance bond after a negative report on the technology was published. The engineering firm soldiered on and now counts 60 North American cascade systems among its installations. Many of them are cold storage facilities, including the 300,000-sq.-ft. U.S. Cold Storage plant in Bethlehem, Pa., that requires less than an 8,000 lb. charge, but a number of food processors also have installed the technology.
One is Oxford Frozen Foods, which uses the technology in a blueberry processing plant in Saint-Isidore, New Brunswick, which opened last year. The facility’s two freezing tunnels process up to 1.5 million lbs. of fresh blueberries a day, with cold storage for 45 million lbs. of product. Energy efficiency and environmentally friendly practices drove the decision to employ cascade, LED lighting and advanced controls.
“In a lot of cases, going green costs a company more,” notes Marshall. “In this instance, going green is just a byproduct of a better operating system.”
Direct comparisons of cascade and ammonia-only refrigeration are hard to come by. A proprietary analysis by a major public utility put the energy savings at 17 percent. Reciprocating compressors are a necessary upgrade from screw compressors, and efficiency gains are contingent on temperature set points: the colder they go, the greater the savings.
Existing ammonia systems can be retrofitted to cascade, although the timeline can stretch to 12 months or more, depending on availability of downtime. Skid-mounted CO2 loops can be commissioned in six months, M&M engineers say.
Continuous vs. batch freezing
Regardless of the refrigerant used, efficiency gains in freezing are possible by rethinking the configuration of the cubic space, particularly when blast cells are involved.
That’s the contention of Dan Tippmann, a partner at Tippmann Innovations (www.ticold.com), Fort Wayne, Ind. His Draw-Thru rack freezing system can freeze pallet loads at half the cost in a fraction of the time of conventional blast cells, Tippmann maintains, but food processors have a healthy skepticism of performance claims. Whereas Marshall posted a performance bond for his first cascade client, Tippmann provides a performance guarantee for his system.
“Air always follows the path of least resistance” is Tippmann’s mantra, and that physics fundamental is the foundation of his system. “We’ve mastered the art of getting air through racks of products” with pallet spacers that facilitate extracting the heat in boxed food. Cased poultry in the core of a pallet can take 60 hours to freeze, he calculates. His design has been shown to lower core temperatures in a cell loaded with pallets of poultry leg quarters to 0°F from 32° in 16 hours.
In addition to pallet spacers, a key element in the design is one-deep racking. Conventional systems pack pallets 4-6 deep, making blast freezing a batch process. When coupled with a warehouse management system, Tippmann’s one-deep design results in a continuous system, allowing workers to rotate out faster-freezing pallets based on required dwell time to reach the desired core temperature. Efficiency isn’t compromised if there are empty pallet positions in the cell, unlike conventional cells.
“Why wait for a batch of 72 pallets to load a cell when you can be continuously loading and increasing turns?” Tippmann rhetorically asks.
The alternative to blast freezing is flash freezing, the term favored by gas companies that provide cryogenic gases and freezing equipment to frozen food manufacturers. One development on that accelerated-freezing front is a pellet and dot freezing system from Praxair Technology Inc. (www.praxair.com), Danbury, Conn.
“Dots are typically 3-4 mm spheres,” explains Rupa Vass, associate director-market development at Praxair, and are deposited directly into an immersion freezer. Pellets are about 1-in. long and pass through a heat exchanger before entering the liquid-nitrogen bath. Whether dots or pellets, they are formed from a slurry of the food product itself, whether it is a sauce, puree or ice cream.
Better portion control of the components of microwavable ready meals is one benefit, Vass writes, allowing processors to meter in specific levels of protein, sauce or other components and accelerating freezing time at the core.
For ice cream, a side stream of 10 percent of the product flow is deep-frozen in the immersion freezer, then added back into the main stream prior to packaging. “This technology reduces the load on existing mechanical refrigeration capacity and significantly improves the quality and shelf life of the product,” according to Vass.
“The technology improves the microstructure of the product and produces approximately 35 percent smaller ice crystals and gas bubbles,” he adds. Smaller crystals and air bubbles enhance creaminess. Dots are no longer discernible after mechanical hardening and don’t impact taste or texture, according to Praxair.
Whether frozen food manufacturers want to improve product quality, boost throughput or drive down operating costs, suppliers are applying the laws of thermodynamics to improve on existing technology to deliver those benefits. Applying those laws in new and innovative ways can help food processors maintain the financial viability of operations.